A turbocharger may be provided in an engine to increase engine torque or power output density. The turbocharger may include an exhaust driven turbine coupled to a compressor via a drive shaft. The compressor may be fluidly coupled to an air intake manifold in the engine connected to a plurality of engine cylinders. Exhaust flow from one or more engine cylinders may be directed to a turbine wheel causing the turbine to rotate about a fixed axis. The rotational motion of the turbine drives an impeller (e.g., wheel) of the compressor which compresses air into the air intake manifold to increase boost pressure based on engine operating conditions.
Compressor efficiency influences overall engine performance and fuel consumption. For example, lower compressor efficiency may result in slow engine transient response and higher fuel consumption for both steady-state and transient engine operation. At lighter engine loads, when compressor efficiency is reduced, increased turbocharger lag may result during a tip-in. Additionally, light load operation may result in lower compressor efficiency and compressor surge limits may restrict boost pressure rise at low engine speeds.
Other attempts to address low compressor efficiency include utilizing a variable inlet compressor that utilize guide vanes to direct and adjust flow through an impeller of the compressor. One example approach is shown by Sconfietti et al in EP2024645. Therein, a variable inlet device disposed adjacent the compressor inlet and including a plurality of vanes is disclosed. Each of the vanes is movable between a first position and a second position to control the quantity of fluid that passes to the impeller. Specifically, the vanes are positioned about a center of a wheel device and pivot about an axis parallel with a central axis of the compressor. In a closed position, flow is blocked from passing to the impeller and in an open position, gas may flow between adjacent blades, around the center of the wheel device.
However, the inventors herein have recognized potential issues with such systems. As one example, even in the open position, due to the orientation and pivoting direction of these vanes, flow through the variable inlet device and to the impeller is restricted (e.g., partially blocked). As a result, this type of variable inlet has reduced high end efficiency and constrains the high end flow with flow restricting issues. Further, this type of device cannot generate pre-swirl flow for the compressor which may increase compressor low-end efficiency.
In some embodiments, the compressor may include an active casing treatment with two separate slots on the compressor shroud, one between full and splitter blades serving as a bleed slot for surge control, and the other slot downstream of the splitter blades serving as an injection slot for choke flow capacity enhancement. These two slots can be covered individually to achieve increased lower end efficiency and surge performance of the compressor, as well as high end choke flow capacity. However, the inventors herein have recognized that the active casing treatment alone may not sufficiently increase the light load compressor flow range and operating efficiency, especially to enable engine downsizing. As a result, engine performance may still be lower than desired.
In one example, the issues described above may be addressed by a compressor, comprising: a casing forming a recirculation passage surrounding an intake passage; an active casing treatment surrounding a wall separating the intake passage and the recirculation passage and adapted to selectively control a flow of gas through a plurality of ports disposed in the wall; an impeller; and an adjustable device positioned in the intake passage, upstream of the impeller, and including a plurality of pivotable and adjacently arranged blades forming a ring. The blades of the adjustable device may be adapted to pivot between an open position and closed position, thereby adjusting the adjustable device into to the open and closed position. In the closed position, outlet ends of the blades overlap more than inlet ends of the blades, thereby creating a flow restriction through the adjustable device and to the impeller. Additionally, the overlapping blades create spiral grooves on inner surfaces of the blades that face the flow of gas in the intake passage. As a result, pre-swirl flow to the impeller is generated. In the open position, the blades are pivoted away from the central axis of the compressor at the outlet end, reducing the overlapping of the blades and reducing flow restriction through the intake passage and adjustable device to the impeller. In this way, the lower end compressor efficiency is increased due to the restricted, pre-swirl flow generated by the adjustable device in the closed position, as well as increasing high end compressor efficiency due to reduced flow restriction when the adjustable device is in the open position.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.